# Newton Raphson for Cap Excitation Look up table

#### iceman11

Joined May 4, 2007
39
good day all,

I am currently design a 3 phase excitation system for an induction generator for a wind turbine.

now, in order to regulate the system voltage i need to switch specific caps (or reactances depending if i use a TCSC etc etc) but i have opted for a purely capacitive scheme.

now in order to determine the difference between the voltage at the terminals, and the load (regulates the SEIG voltage - Self Excited Ind. Gen. ), i will implement voltage sensors, at the load side, and use an opto-isolater, and filter to be inputted to the µC. i will then scale this voltage out of 5 V , and use a difference to find the difference between this and the reference voltage,. then a look up table will be used to find the corresponding capacitance (to inc or dec the cap value at the IG terminals), depending on the voltage difference between ref and sensed (which then goes to a PI controller)

the problem I am experiencing at the moment is obtaining this look up table, i have read in multiple texts that the newton raphson method is used along with various motor parameters, and its eqv circuit

eg "CAPACITIVE VAR CONTROLLERS FOR INDUCTION GENERATORS FOR AUTONOMOUS POWER GENERATION", S.S. Murthy and Bhim Singh p2 (top left)

but i have no clue how to do this, and what it would require??

Thank You (i know that my thread is lengthy lol)

Dushen Nagesur - Final Year Electrical Eng Student - UKZN,South Africa

#### studiot

Joined Nov 9, 2007
4,998
Don't know anything about controlling wind driven turbines.

However the Newton Raphson method is an extrapolation or interpolation method for obtaining intermediate values of a function by replacing it with the tangent at a known point.
This method is not formulaic but iterated to obtain successively better approximations until substitution shows the required accuracy has been achieved.

Are you sure you don't mean Newton's method of divided differences which does have a formula?

#### iceman11

Joined May 4, 2007
39
Don't know anything about controlling wind driven turbines.

However the Newton Raphson method is an extrapolation or interpolation method for obtaining intermediate values of a function by replacing it with the tangent at a known point.
This method is not formulaic but iterated to obtain successively better approximations until substitution shows the required accuracy has been achieved.

Are you sure you don't mean Newton's method of divided differences which does have a formula?
yea, im pretty sure that Newton Raphson is the method that is used, it is said so in numerous texts. the bit that i am struggling with is obtaining the parameters and equations from the eqv circuit, (especially yhe speed and frequency parameters (for eg. do i have to acutally get these from testing before hand, and what will they represent))